Space craft, missiles, and other projectiles are sometimes equipped with steering features that enable the projectiles to provide for their own guidance. Some of such features include various propellant output valves that operate by opening and closing to redirect propellant thrust and thereby steer the projectile.
Valves for propellant redirection are typically lightweight, yet capable of withstanding the hot environment produced by engine gases since engine gas generators may use and exhaust gases at between 2000 and 5000° F. Even if valves are only required to be briefly exposed to hot gases, the valves should be capable of withstanding such high temperatures for their short duty cycles. For this reason, high temperature divert and attitude control valves for space craft, missiles, interceptors, and other craft are sometimes formed from refractory metals that maintain their strength and form at high temperatures. Also, valves and valve components that are not subjected to hot environments are commonly made from refractory metals or other metals that have high strength and are metallurgically sound.
Although care is taken to produce hot gas valves and other valves that are structurally and metallurgically sound, the processes for manufacturing the valves can be somewhat inefficient. Refractory metal hot gas valve components are currently produced by performing electro-discharge machining and grinding processes on large refractory metal plates or bars. The plates and bars themselves are typically fabricated using sintered powder metallurgy processes. Although the valves that are formed from these combined processes are operable at high temperatures, the valve components may include micropores or other inconsistencies that are sometimes products of sintered powder metallurgy processes, and that may affect valve's mechanical integrity if the components are included in the valve. The component inconsistencies require screening prior to manufacturing and/or using a hot gas valve to assure that the valve will operate correctly at high temperatures.
One example of a valve component that is formed from a refractory metal using sintered powder metallurgy processes is a disc that is a component of some hot gas valves that are used in missiles. The disc allows propellant gas to flow out of only one side of the valve or the other. However, if the discs have micropores or other inconsistencies that are sometimes associated with sintered powder metallurgy processes, they can potentially deform or crack at temperatures ranging from room temperature to the elevated operating temperatures.
Since hot gas valves that include discs for gas flow regulation provide some distinct advantages over other valve designs, many efforts have been undertaken to find ways to manufacture refractory metal discs having consistent structural and metallurgical characteristics. One recent manufacturing development includes fabricating a refractory metal-based plate, such as a rhenium-based plate, using layer additive manufacturing (LAM), which is one of many solid-free-form fabrication processes that are increasingly being used to manufacture parts in three-dimensional space by depositing successive layers of material. However, the LAM-formed discs are typically either sufficiently ductile but have low strength, or are sufficiently strong but have low ductility, depending on the refractory metal alloy composition.
Hence, there is a need for methods for manufacturing hot gas valve discs and other valve components that have high ductility and high strength. There is a particular need for methods that manufacture such components with high structural and metallurgical consistency so that the need for inefficient screening methods can be minimized.